Closed cell phenolic foam

ABSTRACT

This invention relates to the manufacture of foam from phenolic resins and to the foam so produced. In order to overcome some of the limitations of the prior art closed cell phenolic foams, we have developed a method of preparing closed cell foams from modified, low cost phenol formaldehyde resoles, which exhibit high closed cell contents, low friability and low thermal conductivity. This specification provides a foam competitive with urethane foams, which have an aged thermal conductivity of about 0.16K. or less, but which will not generate fumes as toxic as those of urethane. There is, provided a method of making a phenolic foam material comprising the steps of 
     (1) preparing a base catalyzed phenol-formaldehyde resole having a mole ratio of phenol to formaldehyde of between 1:3 and 1:4.5 and containing substantially no free phenol but including residual formaldehyde; 
     (2) neutralizing, concentrating and acidifying said resole; 
     (3) reacting with co-reactants consisting essentially of urea and resorcinol in an amount such that the molar ratio of combined urea and resorcinol to free formaldehyde in said resole is about 1:1, the ratio of urea to formaldehyde being selected so that in a test starting at ambient temperature a reaction temperature of 70° to 75° C. is reached during foaming within a period of 4 to 8 minutes, the urea being reacted first where urea and resorcinol are separately reacted with the resole; 
     (4) (a) combining the product of step 3 with a surfactant in an amount sufficient to be effective as a cell stabilizer and 
     (b) a blowing agent in an amount sufficient to form a foam; 
     (5) initiating foam formation by adding to the mixture of step 4 a catalyst comprising an acidic material to reduce the pH of the mixture to below 4; 
     (6) curing the mixture of step 5.

This is a division of application Ser. No. 676,262 filed Nov. 29, 1984,now U.S. Pat. No. 4,546,119.

This invention relates to the manufacture of foam from phenolic resinsand to the foam so produced.

This invention is an improvement with respect to the invention describedin U.S. application Ser. No. 385,260 filed June 4, 1982 by inventors M.H. Rastall, N. H. Ng, and E. J. MacPherson, and the same assignee, andentitled "Modified Phenolic Foams", the contents of which areincorporated herein by reference. In that applicationphenol-formaldehyde foams are prepared from resoles having a highstarting mole ratio of formaldehyde to phenol, and which are essentiallyfree of phenol. Treatment with a formaldehyde scavenger or co-reactantreduces the initially high free formaldehyde content.

It is important for the purpose of producing a foam having a highproportion of closed cells to control the foaming reaction to avoiddisruption of the cell structure, otherwise thermal conductivity will beadversely affected, particularly if a volatile blowing agent is usedhaving a thermal conductivity less than that of air. Thus Gusmer in U.S.Pat. No. 4,303,758 dated Dec. 1, 1981 and entitled "Method of PreparingClosed Cell Phenol-Aldehyde Foam and the Closed Cell Form thus Produced"uses a comparatively low phenol to formaldehyde ratio of 1:2.0 to 3.0 toprovide a resole having a low exothermic heat of reaction.

In accordance with this invention a different approach to that of Gusmerhas been utilized. We use a high starting mole ratio of formaldehyde tophenol. The reaction is controlled by using urea and resorcinol asformaldehyde scavengers in a ratio which will result in a reactiontemperature of 70° to 75° C. being reached in a test of foamingcommencing at ambient temperature within a period of 4 to 8 minutes.

Further improvements are achieved in accordance with other more detailedaspects of this invention by pH adjustment of the resin prior tofoaming, selection of blowing agent, selection and level of surfactant,viscosity control, and control of other variables.

The general object of this invention is to overcome the deficiencies ofprior art methods and materials. These materials have been found to beeither deficient in the maintenance of their closed cell character andthus, long term thermal performance, or one or more property has beendeficient, such as dimensional stability, water absorption, friability,tendency to punk, corrosivity, compressive strength, etc., rendering thematerial unsuitable for commercial use as an insulant.

In other prior art disclosures concerning closed cell phenolics, theproposed preparation relies on uneconomical production methods whichoperate at low speeds.

In order to overcome some of the limitations of the prior art closedcell phenolic foams, we have developed a method of preparing closed cellfoams from modified, low cost phenol formaldehyde resoles, which exhibithigh closed cell contents, low friability and low thermal conductivity.

A further object is to provide a foam competitive with urethane foams,which have an aged thermal conductivity of about 0.16K. or less, butwhich will not generate fumes as toxic as those of urethane.

In accordance with this invention there is provided a method of making aphenolic foam material comprising the steps of

(1) preparing a base catalysed phenol-formaldehyde resole having a moleratio of phenol to formaldehyde of between 1:3 and 1:4.5 and containingsubstantially no free phenol but including residual formaldehyde;

(2) neutralizing, concentrating and acidifying said resole;

(3) reacting with co-reactants consisting essentially of urea andresorcinol in an amount such that the molar ratio of combined urea andresorcinol to free formaldehyde in said resole is about 1:1, the ratioof urea to formaldehyde being selected so that in a test starting atambient temperature a reaction temperature of 70° to 75° C. is reachedduring foaming within a period of 4 to 8 minutes, the urea being reactedfirst where urea and resorcinol are separately reacted with the resole;

(4) (a) combining the product of step 3 with a surfactant in an amountsufficient to be effective as a cell stabilizer and

(b) a blowing agent in an amount sufficient to form a foam;

(5) initiating foam formation by adding to the mixture of step 4 acatalyst comprising an acidic material to reduce the pH of the mixtureto below 4;

(6) curing the mixture of step 5.

There is also provided a phenolic foam material comprising the reactionproduct of

(1) an aqueous solution of a base-catalyzed phenol-formaldehyde resolehaving a mole ratio of phenol to formaldehyde of between 1:3 and 1:4,said solution containing substantially no free phenol, the pH of saidsolution having been adjusted with carbon dioxide to between about 6 and8 and the resulting precipitate having been removed and having beenconcentrated to a viscosity at 30° C. of more than about 15,000centipoises and the pH having been adjusted by the addition of an acidto about pH 3 to 4;

(2) urea and resorcinol, the amount of urea and the amount of resorcinolbeing selected such that the mole ratio of urea and resorcinol toresidual formaldehyde contained in said resole is about 1:1 and theweight ratio of urea to resorcinol is about 2:1 to 3:1.

In one aspect the ratio of phenol to formaldehyde may be above 1:3.1and/or below 1:4.3.

In the drawings,

FIG. 1 is a plot of cure exotherms comparing a urea-resorcinol extendedresole with a urea extended resole.

FIG. 2 shows a plot of cure exotherms for various ratios of urea andresorcinol.

FIG. 3 shows the normalized cure thermogram for phenol-formaldehyderesin extended with urea/resorcinol.

FIG. 4 shows the normalized cure thermogram for phenol formaldehyderesin extended with urea, as a basis for comparison with FIG. 3.

The steps in preparing foams in accordance with the preferred practiceof this invention are as follows:

1. Preparation of resole resin.

2. Neutralize.

3. Filter.

4. Concentrate.

5. Adjust the pH by the addition of an acid.

6. Add urea and resorcinol to the resin.

7. Add a surfactant and a blowing agent.

8. Add acid catalyst and allow to foam.

9. Cure.

Resin Type and Preparation

These foams are prepared from resoles which have been made usingstarting mole ratios of phenol to formaldehyde in the range of 1:3 to1:4.5 and preferably 1:3 to 1:4. Of particular utility are resolesprepared using phenol to formaldehyde starting mole ratios of 1:3.7 withcalcium oxide as the basic catalyst. Resoles of this type have beendisclosed in said U.S. application Ser. No. 385,260, and in U.S. Pat.No. Re. 30,375 of Aug. 19, 1980, of the same assignee, incorporatedherein by reference.

Such high mole ratios are the basis for resins which are, for allpractical purposes, free of phenol and which can be treated with aformaldehyde co-reactant, or a scavenger, in order to reduce theinitially high free formaldehyde content. Nitrogen containingco-reactants are particularly beneficial as they improve fire resistantproperties of the foam.

EXAMPLE 1 Preparation of Preferred Resole Resin

A phenol formaldehyde (P/F) resole resin of P/F charge ratio 1:3.7 wasprepared by loading a reactor with 2,235 gallons of 44% aqueousformaldehyde and 912 gallons of USP 98% phenol. The agitator was startedand the catalyst, 880 lbs, of calcium hydroxide (99% purity) was meteredin over a period of about one hour and thirty five minutes.

The temperature at this point was about 86° F. It was held at 86° F. forabout 25 minutes, then the temperature was allowed to rise to 110° F.for about 28 minutes. The temperature was then allowed to rise to 125°F. in 20 minutes and held at 125° F. for about 40 minutes. Thetemperature was allowed to rise to 150° F. in 50 minutes and held at150° F. for about 55 minutes until the free formaldehyde content droppedto 8.2%. The mixture was cooled to 80° F. and the final pH was measuredas 8.7. Typical properties of this type of resin are given in Table I.

                  TABLE I                                                         ______________________________________                                        TYPICAL RESIN PROPERTIES                                                      Oven Solids % (2 hrs. @ 150° C.)                                                               46.0    Min.                                          Ash % (@ 1500° F.)                                                                             1.7     Min                                           pH                      8.7                                                   % Free Formaldehyde     8.2-8.8                                               Dilutability            ∞                                               Viscosity (@ 30° C.)                                                                           20      cps                                           Specific Gravity (@ 25° C.)                                                                    1.19                                                  TYPICAL COMPONENT ANALYSIS*                                                                           %                                                     Phenol                  .34                                                   o-methylol phenol       .51                                                   p-methylol phenol       .55                                                   total mono-methylol phenols                                                                           1.56                                                  total dimethylol phenols                                                                              2.19                                                  total trimethylol phenols                                                                             22.48                                                 total diphenyls         14.36                                                 heavier components      2.4                                                   ______________________________________                                         The number average molecular weight was found to be 230                       *Data obtained from gas chromatographic analyses of resin sample after        silylization with BSTFA, using 2,4dimethylol-phenol as an internal            standard.                                                                

Neutralizing

The storage stability of the resin is improved by reducing the pH to theregion of 5.5 to 6.5 through the use of a neutralizing acid selected soas to produce a resin which, on concentration, has the characteristicsrequired to generate a closed cell foam.

The following acids were evaluated as resole neutralizing agents:

1. Carbon dioxide gas

2. Phosphoric acid

3. Sulfuric acid

4. Acetic acid

5. Lactic acid

6. Citric acid

7. Oxalic acid

8. Sulfamic acid

Of these acids, carbon dioxide is preferred for three reasons:

1. The insolubility of the calcium carbonate precipitate (where calciumhydroxide has been used as the basic catalyst) facilitates its removalby filtration.

2. The carbonate neutralized resole exhibits desirable reactivityproperties when further catalyzed during foam preparation.

3. The rate of viscosity increase of the carbonate neutralized resoleduring foaming is instrumental in maintaining low blowing agent losses.

The reactivity of the resole when neutralized with these various acidswas assessed in the following manner:

EXAMPLE 2

The resole of Example 1 was first concentrated to 70% oven solids andthen treated with a formaldehyde co-reactant, such as resorcinol andurea. The amount of co-reactant used was sufficient to give a 1:1 moleratio of free formaldehyde to resorcinol and urea.

When the co-reactant had reduced the formaldehyde level in the resin, aknown weight of a 65% aqueous solution of phenol sulfonic acid was addedand the mixture stirred rapidly. The rate of viscosity increase withtime was monitored using a Brookfield viscometer. The results arepresented in Table II.

                  TABLE II                                                        ______________________________________                                        EFFECT OF NEUTRALIZING ACIDS                                                  ON RESOLE ACTIVITY                                                                        Initial Viscosity of                                              Neutralizing                                                                              Resorcinol Extended                                                                           Time to Reach                                     Acid        Resole (25° C.)                                                                        1.8 MM cps                                        ______________________________________                                        Carbon dioxide                                                                            46,300          5 min.                                            Phosphoric  51,400          No appreciable                                                                viscosity increase                                Sulfuric    27,300          3 min. 35 sec.                                    Acetic      25,900          No appreciable                                                                viscosity increase                                Citric      24,550          No appreciable                                                                viscosity increase                                Oxalic      40,200          4 min. 40 sec.                                    Sulfamic    203,000         4 min. 25 sec.                                    ______________________________________                                    

The benefits of carbon dioxide as the neutralizing agent are furtherillustrated in the following Example 3.

EXAMPLE 3

A modified resole (83.9 g) containing resorcinol, urea and about 8% byweight of Pluronic F-127 (trade mark) was mixed with Freon 113 (trademark), in sufficient quantity to produce the desired density. When astable emulsion had been produced, as evidenced by no weight loss, theappropriate amount of catalyst, consisting of a 67% blend of Witco M-100(trade mark) in ethylene glycol, was added and the mixture rapidlystirred before pouring into a 12"×12"×2" steel mold preheated to 80° C.The mold was then sealed and placed in an oven at 80°-90° C. for 15-30minutes. The resultant foam was trimmed, dried at 50° C. for 24 hoursand then placed in a humidity cabinet at 50% R.H. for 24 hours.

The results of preparing foams by this procedure using a modified P/F1:3.7 calcium catalysed resole, neutralized with different acids, aregiven in Table III. From Table III, it can be seen that the best overallfoam properties for these systems, in terms of % closed cells, initial Kand % friability were achieved using carbon dioxide as the resoleneutralizing agent. Oxalic acid, in this instance, gave a high initial Kand a high friability. Carbon dioxide is therefore preferred as theneutralizing agent for the resole resins.

                  TABLE III                                                       ______________________________________                                        EFFECT OF NEUTRALIZING ACIDS                                                  ON FOAM PROPERTIES                                                                                                  %                                       Neutralizing       % Closed  Initial  Friability                              Acid      Foam     Cells     K Value  (as per                                 (Neutralized                                                                            Density  (ASTM     (K=BTU in./                                                                            ASTM                                    to pH 6.5)                                                                              pcf      C.518)    (ft.sup.2 .hr.°F.)                                                              C.421-77)                               ______________________________________                                        Carbon dioxide                                                                          2.87     92        .12      14                                      gas                                                                           Phosphoric                                                                              2.63     18        .25      34                                      Acid                                                                          Sulfuric Acid                                                                           2.92     77         .150    33                                      Acetic Acid                                                                             --       --        --       --                                      Lactic Acid                                                                             --       --        --       --                                      Citric Acid                                                                             2.86      6        .25      56                                      Oxalic Acid                                                                             2.88     91        .19      24                                      Sulfamic Acid                                                                           3.04     50        .25      24                                      ______________________________________                                         Resin P/F 1:3.7 Calcium catalysed  modified with urea and resorcinol as       per Examples 2 and 3                                                     

Filtration

The previous steps of neutralizing together with filtration areillustrated below in Example 4.

EXAMPLE 4

The resole prepared above as in Example 1, was neutralized to pH 6.5with carbon dioxide. The resulting precipitate of calcium carbonate wasfiltered off to reduce the calcium level in the resin to between0.1-0.2%.

Concentration

To generate a closed cell foam from a phenolic resole it is advisable toremove as much volatile material from the resin as in practical. Theconcentration step is illustrated in Example 5.

EXAMPLE 5

The resin resulting from Example 4 was then concentrated toapproximately 82-84% oven solids by passing the filtered resole througha thin film evaporator, operating with a wall temperature of 96° C.under a vacuum of 28 in. Hg°. The estimated residence time of thematerial in the evaporator was 20 seconds, prior to exiting andsubsequent cooling. The resole prepared in this manner had the followingproportions:

    ______________________________________                                        Viscosity @ 30° C. (adjusted to                                                                 22,000 cps                                           78% oven solids)                                                              pH                       7.2                                                  Dilutability %           1100                                                 Free Formaldehyde %      13.5                                                 Calcium content          0.2%                                                 *Free Water % (Karl Fischer)                                                                           1.89                                                 Refractive Index         1.58                                                 No. Average Molecular Weight˜240                                        ______________________________________                                         *Measured at an organic oven solids level of 84.6%.                      

                  TABLE IV                                                        ______________________________________                                        TYPICAL COMPONENT AND EFFLUENT ANALYSIS                                                      Initial P/F Resole                                             Results %      Resole      Conc.   Distillate                                 ______________________________________                                        Phenol         0.62        0.66    0.58                                       o-Methylol Phenol                                                                            0.62        1.03    0.006                                      p-Methylol Phenol                                                                            0.64        1.06    0.008                                      o,p-Dimethylol Phenol                                                                        2.57        4.14    0.01                                       o,o,p-Trimethylol                                                                            22.5        34.21   0.075                                      Phenol                                                                        4,4-Tetramethylol                                                                            16.55       29.10   --                                         Phenol                                                                        Heavier Components                                                                           2.22        14.27   --                                         % Calcium      0.13        0.28    --                                         ______________________________________                                    

Adjustment of the pH by the addition of an acid

The pH of the resole concentrate is adjusted to within the range 3 to 6and preferably 3 to 4 using a suitable acid such as citric acid. This isto establish acidic conditions for the subsequent step of modifying witha co-reactant.

Preparation of a resole modified with a co-reactant

In Examples 6, 7 and 8 which follow, we will illustrate in Example 6preparation of a resole modified with urea, which can be blended withthe resole modified with resorcinol of Example 7. Alternatively, boththe urea and resorcinol may modify the resole in a single stage asillustrated in Example 8. These examples also illustrate the preliminaryadjustment of the pH.

In each of Examples 6, 7 and 8, urea, resorcinol or urea and resorcinolare added to the resole concentrate so as to provide essentially a 1:1mole ratio of co-reactant to residual formaldehyde.

EXAMPLE 6 Preparation of a Urea Extended Resole

The pH of the resole concentrate is adjusted to 3.6 using a 20% citricacid solution. The free water content of the resole is then adjustedwith deionized water, prior to adding powdered urea in sufficientquantity to react with all the free formaldehyde in a 1:1 mole ratio.The mixture is allowed to react at 27° C. to 30° C. until there is noevidence of undissolved urea. The required surfactant may also be addedat this stage. The final urea extended resole typically exhibits a pH ofbetween 5.5 to 6.0 and a viscosity measured at 30° C. of 40,000-100,000cps, depending on the free water content.

EXAMPLE 7 Preparation of a Resorcinol Extended Resole

In this preparation, the resole concentrate is treated with citric acidto reduce the pH and with deionized water to adjust the water content,prior to treatment with sufficient resorcinol to react with theformaldehyde in a 1:1 mole ratio. The mixture is kept below 30° C. untilall the resorcinol has reacted. The final pH is between 5.5 to 5.7 andthe viscosity @30° C. is 60,000 to 100,000 cps.

The materials of Examples 6 and 7 can be blended in appropriateproportions such as from 3 to 4 parts of urea extended resole to 1 partof resorcinol extended resole to give a premix or a urea resorcinolextended resole can be made directly in one step, as in Example 8.

EXAMPLE 8

Preparation of a Urea-Resorcinol Modified Resole

As in the previous Examples 7 and 8, the resole is treated with citricacid to adjust the pH to 3.6 and deionized water is added to give thedesired solids level. Powdered urea is then added to give a ratio of0.82 moles of urea per mole of free formaldehyde. The mixture is stirredat 27°-30° C. until all the urea has dissolved and the free formaldehydeis 1.29%. Then 0.18 moles of resorcinol are added and stirring iscontinued until no undissolved material remains and residualformaldehyde is reduced to 0.31%. For convenience, the desiredsurfactant is usually added during the preparation of the modifiedresole. The actual weight ratio of urea to resorcinol in the example is2.48:1.

Typical properties of this material are a pH of 5.5 to 5.7 and viscosityof 40,000-100,000 cps at 30° C., depending on the water content.

Modified resoles produced by the methods of Examples 6, 7 and 8 can beutilized to prepare closed cell phenolic foams.

The selected resin must have adequate reactivity to produce a degree ofcure sufficient to yield a product that is dimensionally stable at thetemperatures to which it will be subjected during use.

Although resin reactivity can be changed by varying the acid catalystlevel, it is preferred that the acid level be held to a practicalminimum to reduce potential for corrosion problems.

The inherent reactivity of a phenolic resin as we have alreadyillustrated, is due, in part, to the neutralizing acid used in the pHadjustment of the initial resole. Other factors are the chemicalcomponents in the resole and the distribution of those components, thefree water content, and the level of other volatile materials, such asfree formaldehyde and free phenol.

We have found that the modified resoles of the present disclosure can bevaried over a wide range of reactivity by varying the urea/resorcinolratios.

In general, the addition of resorcinol increases the resole reactivitywhile urea moderates reactivity and also provides some improved punkresistance.

To achieve a degree of cure sufficient to ensure dimensional stabilityof the finished product during use, we have found it necessary for theresin reactivity to be such that a reaction temperature of 70°-75° C. isreached in a test of foaming commencing at ambient temperature in aperiod of between 4 to 8 minutes and preferably 6 minutes.

This method of foam preparation is preferred over the alternative methodof precuring a froth at a lower temperature, followed by heat treatmentat an elevated temperature. The former process would lend itself tofaster production speeds with better overall economics.

Resin reactivity was assessed in the following manner: A mixture of 83.9g of P/F resole which was modified with urea and resorcinol andcontained 4.5% free water and 7.7% Pluronic F-127 surfactant, was mixedwith Freon 113 until a stable emulsion containing 6.7 g of F-113 wasobtained. To the emulsion was added 9.4 g of a 67% solution of M-100acid in ethylene glycol and the material was stirred until homogeneous.The reaction mixture was then transferred to an insulated container anda thermocouple was used to measure the rate of change in temperaturewhich was recorded on an xy plotter.

Typically, the maximum temperature achieved starting from an ambienttemperature of about 20° C. under these conditions was between 70°-75°C. in 4 to 8 minutes. This method was used to establish changes inreactivity versus changes in urea/resorcinol ratios, Freon levels andacid levels. Some examples of these plots are illustrated in FIGS. 1 and2. It will be noted that under the specified conditions a weight ratioof urea to resorcinol of about 2:1 to 3:1 was best.

Once a desired formulation is established, minor variations inreactivity from the norm of 70° to 75° C. which occur due to slightdifferences from resin batch to batch, can be accommodated by varyingthe acid level over a narrow range.

In FIG. 1 the formulations were:

    ______________________________________                                        FORMULATION   (1)          (2)                                                ______________________________________                                        P/F Resole (80.9% o.s)                                                                      57.9             55.85                                          Water         1.8              0.18                                           Citric Acid   0.1              0.09                                           Urea          13.4             15.87                                          Resorcinol    5.5              --                                             Pluronic F127 4.9              0.82                                           Freon 113     6.8              9.07                                           M100          9.6    (in EG)   18.13                                                                              (in DEG)                                  ______________________________________                                         EG = ethylene glycol                                                          DEG = diethylene glycol                                                  

In FIG. 2 the formulations were:

    ______________________________________                                        Sample                        Wt. Ratio                                       No.     % P/F/U     % P/F/R   Urea:Resorcinol                                 ______________________________________                                        1       80          20        2.53:1                                          2       70          30        1.48:1                                          3       60          40        0.95:1                                          4       50          50        0.64:1                                          5       40          60        0.42:1                                          6       90          10        5.73:1                                          ______________________________________                                    

As mentioned above in the discussion of the reactivity of theco-reactant, it is considered important to understand and control therate of exothermic reactions during foaming, in order to produce closedcell foams.

The resoles having the formulations indicated above were used togenerate foams for exotherm studies. These plots are shown in FIGS. 1and 2.

Increasing the resorcinol level as shown in FIG. 2 leads to a more rapidheat build up in the initial reaction stage. However, for the higherresorcinol level, the peak temperature is too high and will lead torupture of the cells, due to excessive pressure produced by the watervapour.

Comparison of the time-temperature profiles shown in FIG. 1 illustratesthe preferred temperature increase for the urea/resorcinol modifiedresole foam. In this example, the more rapid exotherm in the initialreaction stage is accompanied by an increased viscosity compared to theurea extended resole. Table V illustrates the comparative properties ofthese two foams.

                  TABLE V                                                         ______________________________________                                        COMPARISON OF                                                                 P/F/U AND P/F/U/R MODIFIED FOAMS                                                             Urea         Urea Resorcinol                                                  Extended Resole                                                                            Extended Resole                                   Property       (P/F/U)      (P/F/U/R)                                         ______________________________________                                        Density (pcf)  3.01         2.83                                              % Closed Cells 0-13         94                                                % Retained FREON                                                                             0            5.3                                               % Friability   80           15                                                Residual Cure  25.7         17                                                (cal./g)                                                                      ______________________________________                                    

The residual cure is determined on preconditioned samples usingDifferential Scanning Calorimetry. In this method, a sample is placed ina sealed pan to prevent loss of volatiles and subjected to apreprogrammed temperature rise of 10° C./min. Under these conditions, anexothermic peak is obtained when any further cure of the materialoccurs. The area under the curve is taken as a measure of the residualcure of the foam. The normalized cure profiles or thermograms for theP/F/U and P/F/U/R modified resoles are illustrated in FIGS. 3 and 4.

Addition of Surfactant and Blowing Agent

As indicated in Examples 6 and 8 the surfactant is usually, forconvenience, added during preparation of the resole. The use of asurfactant is important to the production of a commercially acceptablephenolic foam. We have found that the type and concentration ofsurfactant are major factors in producing good closed cell foams.

The prior art describes the use of many types of surfactants which aresuitable for use. Nonionic, cationic and even anionic types have beenclaimed. To produce closed cell foams which contain the blowing agent insufficient amounts to given superior thermal values, (as compared to airfilled materials). Careful selection of resin and surfactant propertiesis required. In addition, the level of surfactant is important,providing viscosity control of the reacting material, thus preventingpremature drainage and thinning of the cell windows during the initialfoam forming process. This phenomenon is well known and is described invarious tests as the Gibbs and Marangoni effects.

We have found that the Pluronic (trade mark of BASF Wyandotte) typenon-ionic surfactants are particularly suited to our system. Ofparticular utility are the higher molecular weight F-127, F-108 and F-98polyethylene-polypropylene oxides, which, although difficult todisperse, tend to form very stable emulsions with Freons and which arequite insoluble in Freons. Polyethylene oxides or polypropylene oxidescould also be used.

Surfactant concentrations can vary from 2 to 10% of the totalformulation weight. The preferred level for the modified resoledescribed herein is 6-8%.

EXAMPLE 9

The influence of surfactant level on foam properties is illustrated inTable VI. In these examples, a preferred surfactant, Pluronic F-127, apolyethylene-polypropylene oxide was utilized after experimentation witha large variety of surfactants. Pluronic F-127 indicated that it wouldprovide superior performance in our particular resin system with regardto viscosity control, friability, closed cell content, initial thermalperformance and maintenance of thermal performance.

In Table VI it can be seen that as the level of surfactant is increased,the viscosity of the resole blend also increased with surprising changesto the initial K, friability and closed cell contents. A viscosity above30,000 cps at 30° C. is therefore preferred.

                                      TABLE VI                                    __________________________________________________________________________    INFLUENCE OF SURFACTANT CONCENTRATION ON FOAM PROPERTIES                      Surfactant Level                                                              Based on P/F Resole                                                           (Pluronic F-127                                                                          Viscosity of Blend                                                                     Initial K                                                                          % Friability                                                                           % Closed Cells                              from BASF) @ 30° C. (cps)                                                                  value                                                                              (ASTM C. 421-77)                                                                       (ASTM C. 518)                               __________________________________________________________________________    2          20,000-25,000                                                                          .123-.126                                                                          43       85                                          4          30,000-40,000                                                                          .110-.115                                                                          30       92                                          10         46,000-50,000                                                                          .107-.118                                                                          15       92                                          __________________________________________________________________________     P/F 1:3.7 Calcium catalysed resole modified with urea and resorcinol.    

The blowing agent must be added prior to foaming.

Any of the more common Freon blowing agents can be used to expand aphenolic resole. However, since we wish to lay down a liquid mixtureonto a board-forming conveyor, as opposed to a froth, we prefer to useFreon-113 which normally boils at 47.6° C. We have found that, bycareful selection of resin and surfactant properties, the Freon can bereadily incorporated to produce a stable emulsion. This stable emulsionis such that minimal Freon losses occur during the expansion process.The Freon level can be varied over a wide range from 5 to 15%.

For the modified resoles as described herein, we prefer to use a 7%concentration of blowing agent to produce closed cell foams in thedensity range of 2.5 to 3.0 pcf with initial thermals of 0.10 to 0.11K.

Foaming

The next step is the initiation of foam formation with a catalyst.

In the preparation of phenolic foams, acid catalysts are used toinitiate the exothermic curing reactions. In general, any acid capableof reducing the pH of the resole to between 1 to 4 and preferablybetween 2 and 3, will be suitable. In practice, not all of the commonacids are used in spite of claims to the contrary. For example,hydrochloric acid is known to provide a very fine celled foam, but italso has potential to react with formaldehyde formingbis-chloromethylether, a carcinogen. Sulphuric, a very strong acid, isdifficult to disperse in the resole and requires dilution to preventlocal gelation from occurring. For these and other reasons, the organicsulfonic acids are preferred.

We prefer M-100 or Ultra TX (Trademarks of the Jim Walters Corp andWitco Chemicals) mixtures of toluene and xylene sulfonic acids, dilutedin glycols to catalyse the cure of our modified resoles.

Curing

During the preparation of phenolic foams, volatiles are produced as aresult of the condensation reactions which occur on crosslinking. Thesevolatile materials, which comprise mainly water and formaldehyde must beremoved during the drying and post curing process to produce adimensionally stable product. The temperature at which this conditioningis carried out is selected so as to produce no significant deteriorationin closed cell content, due to rapid release of these volatiles. Oncethe moisture content is reduced to a level consistent with the ambientmoisture, the drying process is terminated.

Upon completion of this drying process, the thermal properties shouldshow no further deterioration under the maximum temperature conditionsencountered during use.

The upper service temperature for phenolic foam based insulationproducts, for example roof insulation, is about 80°-90° C. (176°-194°F.). Heating the product to 120° C. guarantees that the thermalproperties will be maintained in typical service environments.

The following Table VII illustrates the thermal stability achieved as aresult of treatment of the product at a temperature of 50° C. for 24hours. It will be noted that treatment for further periods of time atsuccessively higher temperatures did not result in a significantdecrease in closed cell content. If on the other hand, the product hadbeen subjected to a temperature as high as, say 100° C. without thepreliminary treatment at 50° C., there would have been extensiverupturing of cells.

                  TABLE VII                                                       ______________________________________                                        CLOSED CELL CONTENTS VS. HEAT TREATMENT                                       Temperature (°C.)                                                                    Time (hrs)                                                                              Closed Cell Content %                                 ______________________________________                                        50            24        95.0                                                  60            22        94.1                                                  78            22        93.9                                                  80            20        95.0                                                  100           25        93.8                                                  120           22        92.0                                                  ______________________________________                                    

Properties of the foam produced in accordance with this invention andfurther modification of such properties.

A multiplicity of tests are used to assess the properties and thussuitability of these closed cell foams as potential commercialinsulating materials. It is believed that the most relevant propertiesare:

1. Compressive strength

2. Initial Thermals (K values)

3. Aged Thermals (═° C., 20% R.H.)

4. Density

5. Moisture Absorption

6. Flammability

7. Thermal and Dimensional Stability

8. Friability

9. Corrosivity

Variations in thermal properties (K drift), moisture absorption, thermalstability and friability are among the chief areas of deficiency ofprior art phenolic forms.

The following examples serve to illustrate the improvements in theseproperties in accordance with the preferred aspect of this invention.

Initial Thermal Properties

An open celled phenolic foam typically has a K value of 0.21 to 0.25 BTUin./hr.ft² °F. when measured in accordance with ASTM C.411. The lowervalue is achievable only for very fine celled materials. These valuesare due to the presence of air in the foam structure.

Entrainment of blowing agent in the foam cells, particularly fluorinatedhydrocarbons, pentane, cyclohexane, etc., can produce a significantreduction in this K value. The actual K values achieved will be relatedto the type and amount of blowing agent in the cells and the vapourpressure of the material.

Foams of the present invention containing 4-6% by weight of afluorinated blowing agent, such as trichlorotrifluoroethane Freon®113can exhibit K values of 0.11 to 0.12. In particular, foams preparedusing Formulation 2 described below have an initial K value of 0.12(after removing the moisture by drying for 24 hours at 50° C.), withretained blowing agent levels of 5 to 5.4%.

Aged Thermal Values

Ageing of these closed cell materials is a term used to describe theupward drift in K values with time. This drift in K value is well knownin urethane foams and is considered to be due to two main factors. Inthe initial stages, gas diffusion into the foam, in the form of nitrogenor oxygen, occurs to equilibrate the pressure within the cellularstructure. The presence of these gases along with the residualfluorocarbon type blowing agent produces an increase in the K value.

In addition, it is thought that some diffusion of the gaseous blowingagent out of the cells can occur, causing a further gradual increase inthe K value. While both processes probably occur, we have found thatthese rates of diffusion can be significantly retarded, so that thechange in K can be minimized. This will provide superior insulationproperties over the lifetime of the foam in its end use application.

The following formulations serve to illustrate this K drift.

EXAMPLE 10

    ______________________________________                                        FORMULATION 1           % By Weight                                           ______________________________________                                        P/F Resole (79.8% O.S.) (see Example 1)                                                               60.89                                                 Urea                    13.17                                                 Resorcinol              2.55                                                  o-cresol                2.50                                                  Freon 11B/113 60/40 ratio                                                                             6.70                                                  67% M-100.sup.+  in Ethylene Glycol                                                                   7.98                                                  Water                   1.35                                                  Citric Acid H.sub.2 O   0.10                                                  *Pluronic F-127         4.85                                                  ______________________________________                                    

A foam made using this formulation exhibited the following properties:

    ______________________________________                                        Density              2.9 pcf                                                  Closed Cells         87%                                                      Retained Blowing Agent                                                                             1.0%                                                     Initial K Value      0.136 BTU in./hr.ft.sup.2  °F.                    ± Aged K value (after 8 days) at 50° C.                                                  0.18                                                     Closed Cell Content (after 10 days at                                                              85%                                                      50° C.)                                                                Retained Blowing Agent                                                                             <0.2%                                                    ______________________________________                                         + - M100 is a commercially available mixture of toluene and xylene            sulfonic acids manufactured by the Jim Walter Corporation.                    ± - Stored at 50° C.                                           

EXAMPLE 11

    ______________________________________                                        FORMULATION 2                                                                 ______________________________________                                        P/F resole (80.2% O.S)                                                                             60.94                                                    Urea                 12.11                                                    Resorcinol           3.92                                                     Freon 113            6.67                                                     67% M-100 in Ethylene Glycol                                                                       9.44                                                     Water                1.99                                                     Citric Acid H.sub.2 O                                                                              0.1                                                      Pluronic F-127       4.83                                                     ______________________________________                                    

A foam made using this formulation exhibited the following properties:

    ______________________________________                                        Density               3.0 pcf                                                 Closed Cells          93%                                                     Retained Blowing Agent                                                                              5.36%                                                   Initial K Value       0.12 BTU in./hr. ft..sup.2  °F.                  Aged K Value (after 8 days at 50° C.)                                                        0.11                                                    (after 100 days at 50° C.)                                                                   0.12                                                    Retained Blowing Agent                                                                              5.2%                                                    ______________________________________                                    

Foams made according to Formulation 2 exhibit a very low rate of K driftrelative to those made using Formulation 1.

EXAMPLE 12 Moisture Absorption

Moisture uptake in cellular materials causes a decrease in the thermalinsulation efficiency. In open celled foams, this moisture ingress canbe as high as 25%, since the structure is readily permeable to watervapour. In closed cell phenolic foams, absorption of water vapour canoccur if hydrophilic materials are present within the structure.

Careful selection of components used to make the foam can significantlyalter the level of water vapour absorbed at any particular humidity.

To illustrate this phenomenon, various materials can be incorporatedinto the foam formulation. After preparation and curing, the foamsamples are ground into powders and dried to constant weight at 50° C.The samples are then placed in a humidity chamber at 80% R.H. and 25° C.The % moisture uptake (as % weight gain) is measured after 24 hours. Theresults of some studies on acid and glycol variations are presentedbelow in Table VIII. We have found that substitutions of diethyleneglycol for the ethylene glycol diluent initially used leads to improvedmoisture resistance for our foam.

                  TABLE VIII                                                      ______________________________________                                        INFLUENCE OF VARIOUS                                                          ACIDS AND GLYCOLS ON MOISTURE UPTAKE                                                              Sulfuric M-100                                            Acid Concen-                                                                           M-100      67% in   67% in Di-                                                                            M-100 No                                 tration in                                                                             67% in Ethy-                                                                             Ethylene ethylene                                                                              Ethylene                                 Foam     lene Glycol                                                                              Glycol   Glycol  Glycol                                   ______________________________________                                               % Moisture Uptake                                                      0.04 mol. %                                                                            9.4        5.1      5.0     6.8                                      0.03     7.1        4.0      4.4     5.8                                      0.02     7.0        3.5      4.1     4.9                                      0.01     4.3        5.0      4.8     4.2                                      ______________________________________                                    

EXAMPLE 13

In a second series of experiments, the effect of changing thesurfactants on moisture uptake was studied. The results are shown inTable IX.

                  TABLE IX                                                        ______________________________________                                        INFLUENCE OF SURFACTANT TYPE                                                  AND LEVEL ON MOISTURE UPTAKE                                                            % Moisture Uptake                                                             Surfactant levels (Based on Resole Solids)                          Surfactant  10              5     2                                           ______________________________________                                        #DC-193     8.2             --    --                                          ± BRIJ-96                                                                              7.4             --    --                                          *NIKKOL PBC-44                                                                            7.1             --    --                                          °PLURONIC F-127                                                                    9.4             8.2   7.9                                         ______________________________________                                         # - Dow Corning polyalkyl siloxane polyoxyalkylene copolymer surfactant       ± - I.C.I. Americas Inc.  polyoxyethylene oleyl ether surfactant           *  (trade mark) of NIKKO Chemicals, polyoxyethylenepolyoxypropylene cetyl     ether surfactant.                                                             ° - (trade mark) of B.A.S.F.  polypropylene oxide polyethylene         oxide surfactant.                                                        

Friability

Normally, unmodified phenolics are inherently brittle materials. Thisproperty is reflected in their poor resistance to abrasion when formedinto cellular products. Another factor which contributes to the poorfriability of prior art materials is the large cell size encountered intypical phenolic resole open celled and indeed, some closed cellmaterials.

We have found that by selection of resin and formulationcharacteristics, we can produce a significant improvement in thisproperty.

In particular, we have found that the level of surface active agent canhave a pronounced influence on friability. See, for example, Table V.

In addition, we have found other materials can be successfullyincorporated into the formulation to further improve the friabilitywithout detriment to the thermal properties.

    ______________________________________                                        Material          Level    % Friability                                       ______________________________________                                        +POLYVIOL M13/40  2 parts  14                                                 *PIOLOFORM BL-16  2.19 parts                                                                             10                                                 ______________________________________                                         + - (trade mark)  a polyvinyl alcohol supplied by Wacker Chemie               *  (trade mark)  a polyvinyl formal supplied by Wacker Chemie.           

In accordance with this invention a phenol formaldehyde foam materialcan be made having a closed cell content of at least 85%; a closed cellcontent after being heated for 24 hours at 120° C. of 85%; a friabilityof between about 5 and 15%; an initial thermal conductivity of below0.12 BTU inch/ft² h°F.; an aged thermal conductivity of less than 0.14BTU inch/ft² h°F. after 100 days at 50° C. and 20% relative humidity; adensity of between about 1.75 and 2.75 pcf; and a moisture uptake at 25°C. and 80% relative humidity of less than 10%.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A phenolic foam materialcomprising the reaction product of:(1) an aqueous solution of abase-catalyzed phenol-formaldehyde resole having a mole ratio of phenolto formaldehyde of between 1:3 and 1:4, said solution containingsubstantially no free phenol, the pH of said solution having beenadjusted with carbon dioxide to between about 6 and 8 and the resultingprecipitate having been removed, and having been concentrated to aviscosity of 30° C. of more than about 15,000 centipoises; and the pHhaving been adjusted by the addition of an acid to about pH 3 to 4; (2)urea and resorcinol, the amount of urea and the amount of resorcinolbeing selected such that the mole ratio of urea and resorcinol toresidual formaldehyde contained in said resole is about 1:1 and theweight ratio of urea to resorcinol is about 2:1 to 3:1 in the presenceof a surfactant and a blowing agent.
 2. A phenolic foam materialaccording to claim 1 comprising a resole formed from phenol andformaldehyde in the mole ratio of 1:3 to 1:4 co-reacted with urea andresorcinol in the weight ratio of about 2:1 to 3:1, and in the moleratio of urea and resorcinol combined to residual formaldehyde in theresole of about 1:1, said phenol foam material having a closed cellcontent of at least 85%, a closed cell content after being heated for 24hours at 120° C. of 85%, a friability of between about 5 and 15%; aninitial thermal conductivity of below 0.12 BTU inch/ft² h°F., an agedthermal conductivity of less than 0.14 BTU inch/ft² h°F. after 100 daysat 50° C. and 20% relative humidity; a density of between about 1.75 and2.75 pcf; and a moisture uptake at 20° C. and 80% relative humidity ofless than 10%.